scd:p15: Support signing with CardOS 5 cards.

* scd/app-help.c (app_help_get_keygrip_string_pk): Add optional arg
r_pkey and change all callers.
(app_help_get_keygrip_string): Ditto.
* scd/app-p15.c (struct cdf_object_s): Use bit flags
(struct aodf_object_s): Ditto.  Add field 'fid'.
(struct prkdf_object_s): Ditto.  Add fields keygrip, keyalgo, and
keynbits.
(parse_certid): Allow a keygrip instead of a certid aka keyref.
(read_ef_aodf): Store the FID.
(keygripstr_from_prkdf): Rename to ...
(keygrip_from_prkdf): this.  Remove arg r_gripstr and implement cache.
Change callers to directly use the values from the object.  Also store
the algo and length of the key ion the object.
(keyref_from_keyinfo): New. Factored out code.
(do_sign): Support SHA-256 and >2048 bit RSA keys.
common/scd:p15: Support signing with CardOS 5 cards.
* common/util.h (KEYGRIP_LEN): New.
--

This has been tested with a D-Trust card featuring 3072 bit keys.
Note that non-repudiation key for a qualified signature does not yet
work because we do not yet support rsaPSS padding.  Thus a gpgsm
--learn shows a couple of Bad Signature errors for this key.

Signed-off-by: Werner Koch <wk@gnupg.org>

Back ported from master:
- Removed do_with_keygrip
- Added KEYGRIP_LEN
- app_help_get_keygrip_string_pk actually added.
- Move keygrip_from_prkdf in do_sign before the verification.
  It used to work in master only because there it is implictly
  called prior to signing by do_with_keygrip

Signed-off-by: Werner Koch <wk@gnupg.org>

scd/app-dinsig.c

@@ -137,7 +137,7 @@ do_learn_status (app_t app, ctrl_t ctrl, unsigned int flags)
       ksba_cert_release (cert);
       return err;
     }
-  err = app_help_get_keygrip_string (cert, hexkeygrip);
+  err = app_help_get_keygrip_string (cert, hexkeygrip, NULL);
   if (err)
     {
       log_error ("failed to calculate the keygrip for FID 0x%04X\n", fid);